VAX 11/730 quickie

tony duell ard at
Sat Feb 20 06:53:58 CST 2016

> Just started working on mine - been a back-burnered project for a long
> time. Unfortunately all the cables were cut when it was dismantled; I
> was lucky to grab just the CPU.

I had to re-fit all the cables on mine (a painful job), but at least I had them
all, uncut.

> Got it powered up ok - no drama there. I faked cables to the port on

Are all 3 LEDs on the PSU distribution board (under the transparent cover
at the top rear of the PSU) glowing? If not, you have a PSU problem.

> the WCS which drives the console and hooked up my trust VT220 at 2400
> baud. Nada. No self-test prompt; no ROM> prompt.

The oriignal console cable was a straight through ribbon cable with a header
socket (to fit the WCS board) at one end and a DB25 plug at the other. It plugs
into a filter module on the distibution panel, again straight through with a DB25
plug on the outside. This is wired as a DTE (terminal), you need a null modem
cable. Only pins 1,2,3,7 are used, the official cable (I had to make a copy of it)
wires 1 and 7 straght through, swaps 2 and 3 and swaps 6 and 20, but you don't
need the last pair.

Have you set the DIP switch on the WCS board correctly? You can certainly have 300,
1200,2400 or 9600 baud. IIRC some of the other switches do very odd things, so make
sure they are set as the manual says.

I assume you have checked you are plugged into the console port and not the 
remote diagnostic port.

> Maybe I've messed up the faked console cable; I'll check - already
> tried obvious things like making sure Rx & Tx were crossed (it's a
> three wire cable according to the schematics - Rx Tx Gnd; no flow
> control). But I'd like to know more about the assorted LEDs on the CPU
> boards; maybe there's a clue there if it's not getting far enough into
> the self-test to display console output. There's a fair few LEDs on
> the M8391. But the doc I've looked through on Bitsavers doesn't seem
> to document their meanings and interpretations. Can anyone help on
> that point?

They're shown on page 208 of the printset on bitsavers. They display
the memory controller microcode address (nothing to do with the CPU
microcode, the memory controller has its own ROM firmware). I don't
think the memory controller is used by the console ROMs, so I doubt
if this is the problem.

Start by checking the power supply rails (if you haven't already done so),
then see if the 8085 console processor is running, and if it tries to access
the console serial chip.


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